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PDF AD8240 Data sheet ( Hoja de datos )
| Número de pieza | AD8240 | |
| Descripción | LED Driver/Monitor | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de AD8240 (archivo pdf) en la parte inferior de esta página. Total 12 Páginas | ||
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FEATURES
PWM input for LED brightness control
Open LED detection
Latch-off overcurrent protection
Constant voltage regulated output
Supply range: 9 V to 27 V
Regulated voltage range: 12.5 V to 27 V
Operating current: 300 µA
Shutdown current: 10 µA
Temperature range −40°C to +125°C
8-lead MSOP package
GENERAL DESCRIPTION
The AD8240 LED driver/monitor, in combination with an
external transistor, supplies a constant 12 V to drive LED
lamps. This allows cost-effective LED lamp monitoring and
short-circuit protection. The output is regulated at 12 V when
the supply voltage is between 12.5 V and 27 V.
A CMOS compatible, level-dependent, digital input can be used
for PWM control of the LED brightness. VO is turned on when
the PWM input is high and turned off when the input is low.
The AD8240 is designed to work with a PWM frequency up
to 500 Hz, and a typical PWM range from 5% to 95%.
Open LED detection is accomplished by measuring the change
in LED lamp current caused by an open LED(s) through the use
of an internal high-side current-sense amplifier that amplifies
the voltage across an external current shunt. The voltage across
the shunt resistor is amplified to a level that can be measured by
a microcontroller A/D converter or a comparator. The ability to
measure the change in LED lamp current is the key benefit of
constant-voltage LED lamp driving.
The output is current-limited by latching off the output voltage
when the current reaches a preset level. The current limit is set
by selecting the value of the external current shunt that causes
the output of the sense amplifier to slightly exceed the 5 V
reference level when the current exceeds a maximum level.
When the sense amplifier output exceeds 5 V, it trips an internal
comparator that causes the driver to latch off the output voltage.
The latch is reset during the next PWM cycle. The overcurrent
condition can also be detected by a microcontroller or external
comparator by measuring the sense amplifier output.
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
LED Driver/Monitor
AD8240
FUNCTIONAL BLOCK DIAGRAM
VPLUS SHUNT BASE
56
7
VO
8
VSENSE 1
RSENSE
10kΩ
5V
REFERENCE 2
PWM 3
AD8240
LATCH-OFF
DRIVER
R1
350kΩ
R2
250kΩ
4
GND
Figure 1.
PRODUCT HIGHLIGHTS
1. Partial LED lamp failure detection.
Allows for compliance with automotive regulations
for turn signal functionality detection and minimum
brightness, as well as running/brake light minimum
brightness compliance.
2. Current limiting/latch-off protection.
Limiting and latching off the LED current protects vehicle
wiring and prevents lamp damage
3. PWM input.
Provides brightness control.
4. Constant voltage output.
Saves cost by minimizing wiring and system design
complexity.
5. Drives an external transistor for low power operation.
Providing for an external power transistor allows the
AD8240 to be a low cost solution in a small package. A
more efficient design is made possible when the system
designer can select a power device with specifications
that match the application requirements.
6. Linear regulation.
Minimizes EMI, which allows faster system integration,
qualification, and time to market. Additionally, costs are
reduced by eliminating the inductor required for a
switching design. Because of the power-saving nature of
LED lamps as compared to incandescent lamps, a
switching driver is typically not required.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.326.8703 © 2004 Analog Devices, Inc. All rights reserved.
1 page  
PRODUCT DESCRIPTION
The AD8240 consists of four functional blocks labeled A
through D, as shown in Figure 2.
VPLUS SHUNT BASE
VO
VSENSE
B
C
5V
REFERENCE
A
PWM
D
AD8240
GND
Figure 2. Simplified Functional Block Diagram
Table 3 briefly describes the blocks, while the sections that
follow provide more detailed information.
Table 3.
Block
A
B
C
D
Description
Linear regulator
High-side current-sense amplifier
Comparator
Driver
LINEAR REGULATOR (BLOCK A)
The simplified architecture of the linear regulator block is an
amplifier and resistor divider. One input to the amplifier is
tied to the 5 V reference. The other input is tied to a resistor
divider that sets the ratio of the 5 V reference to VO. As a
result, the accuracy of the voltage output is proportional to
the accuracy of the 5 V reference. For example, if the 5 V
reference is 5% high (5.25 V), the output is 5% high (12.6 V).
AD8240
HIGH-SIDE CURRENT-SENSE AMPLIFIER WITH
OPEN LED DETECTION (BLOCK B)
This amplifier is used to measure the LED current by ampli-
fying the voltage across a user-selected shunt resistor. It has a
gain of 24 and an overall accuracy of 5%. The output of the
amplifier is typically connected to a microcontroller A/D
converter input so that the condition of the LED lamp can be
determined. This output can also be tied to other devices such
as a latching comparator or output buffer. It is important to note
that the output of this amplifier has a relatively high impedance
of approximately 10 kΩ. As a result, a buffer amplifier should be
used if the load is less than 100 kΩ.
COMPARATOR WITH LATCH-OFF OVERCURRENT
PROTECTION (BLOCK C)
This block is used to shut down the output in the case of a
short circuit or an overcurrent condition. When the output
of the high-side current-sense amplifier approaches 5 V, the
comparator output switches, causing the driver to latch off the
output voltage.
INTELLIGENT DRIVER (BLOCK D)
The intelligent driver provides multiple functions:
• Level shifts and conditions the output of the regulator
amplifier to drive an external user-selected power
transistor.
• Accepts PWM input so that LED brightness can be
controlled by a user-supplied PWM signal.
• The PWM input can also be used as a simple on/off
control for applications that do not require variable
brightness.
• Latch-off input that latches the output off when the
comparator trips during an overcurrent event. The latch
is reset by cycling the PWM input.
Rev. 0 | Page 5 of 12
5 Page 
ORDERING GUIDE
Model
AD8240YRM
AD8240YRM-REEL
AD8240YRM-REEL7
Temperature Range
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
Package Description
8-Lead MSOP
MSOP, 13” Tape and Reel
MSOP, 7” Tape and Reel
Package Option
RM-8
RM-8
RM-8
AD8240
Package Outline
JTA
JTA
JTA
Rev. 0 | Page 11 of 12
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet AD8240.PDF ] | |
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